As to a conventional coating apparatus that has a coating die for coating a coating solution (paste) on a sheet (web), it is common way to fill up the paste in the discharge path of the coating die in order to remove air from the path, before coating with the coating die. If this deaeration process is not completely done, the paste contains the air and there are bubbles in the coated surface, thereby leading the coating defect.
When filling up the paste and removing the air, the paste is continuously discharged and the paste flows down from the discharge opening of the coating die. If the paste flows into the other devices located around the die, the paste may cause the failure thereof. If the paste is dried off around the discharge opening of the die, the dried-out paste may be attached to the web as a foreign matter and lead the coating defect.
Especially if the web (object to be coated) is an electrode web used in a battery, a foreign matter would be contained in the battery, and may occur defects such as an internal short-circuit.
To solve the above-mentioned problems, it is required for the coating apparatus to provide a good recovery of the paste that is flowed down when filling up the paste and deaerating for the ready-to-coat.
For instance, JP 2003-88791 A discloses a coating apparatus which has a nozzle for coating and the nozzle is connected with a paste storage via a capillary passage, and in which the paste storage has an opening in the vicinity of discharge openings of the nozzle. Due to the structure, the paste flowed down from the discharge openings can be recovered by the storage.
However, the coating apparatus of JP 2003-88791 A uses the capillary action for coating, so that the fine adjustment of the coating condition, such as the distance between the nozzle and the web or the discharging volume, is difficult and therefore the coating defect may be easily occurred. Especially, in such a case that the thin and even paste layer needs to be formed on the web, the fine adjustment is important. Thus, there is a limit to use the technique disclosed in JP 2003-88791 A.
Further, the paste discharged from the discharge openings is recovered to the paste storage, which can improve the usability of the paste, but the foreign matter (grit and dust) may be mixed in the paste during the recirculation. When the paste is coated on the electrode web of the battery, the foreign matter occurs the defect, so that the coating solution is preferably recovered as the waste, or recovered and processed for reuse, whereby the technique of JP 2003-88791 A is not applicable.
Citation List
Patent Literature
PTL 1: JP 2003-88791 A